Various electronic postage meter systems have been developed, as for example, the systems disclosed in U.S. Pat. No. 3,978,457 for Microcomputerized Electronic Postage Meter Systems, U.S. Pat. No. 3,938,095 for Computer Responsive Postage Meter, European Patent Application No. 80400603.9, filed May 5, 1980, for Electronic Postage Meter Having Improved Security and Fault Tolerance Features, U.S. Pat. No. 4,301,507, for Electronic Postage Meter Having Plural Computing Systems, and copending application Ser. No. 447,815, filed Dec. 8, 1982 now U.S. Pat. No. 4,579,054, for Stand-Alone Electronic Mailing Machine.
Generally electronic postage meters include some form of non-volatile memory capability to store critical postage accounting information. This information includes, for example, the amount of postage remaining in the meter for subsequent printing and the total amount of postage already printed by the meter. Other types of accounting or operating data may also be stored in the non-volatile memory, as desired.
However, conditions can occur in electronic postage meters where information stored in non-volatile memory may be lost. A total line power failure or fluctuation in voltage conditions can cause the microprocessor associated with the meter to operate erratically and either cause erasure of data or the writing of spurious data in the non-volatile memory. The erasure of data or the writing of spurious data in the non-volatile memory may result in a loss of critical accounting information. Since the accounting data changes with the printing of postage and is not permanently stored elsewhere, there is no way to recapture or reconstruct the lost accounting information. Under such circumstances, it is possible that a user may suffer a loss of postage funds.
To minimize the likelihood of a loss of information stored in the non-volatile memory, various approches have been adopted to insure the high reliability of eectronic postage meters. It is known from aforementioned U.S. Pat. No. 3,978,457 and aforementioned copening application Ser. No. 447,815 now U.S. Pat. No. 4,579,054 to provide a microprocessor controlled electronic postage meter having memory architecture which includes a temporary storage memory for storing accounting data reflecting each meter trasaction and a non-volatile memory to which the accounting data is transferred during the power down cycle of the meter.
Another approach for preserving the stored acounting data has been the use of redundant non-volatile mmories. One such redundant memory system is disclosed in patent application Ser. No. 343,877, filed Jan. 29, 1982, now abandoned, in the name of Frank T. Check, Jr., and entitled Eletronic Postage Meter Having Redundant Memory. With such redundant memory system the two redundant non-volatile memories are interconnected with a microprocessor by way of completely separate data and address lines to eliminate error conditions. The data may be applied to the memories simultaneously or sequentially at different times. Such a system minimizes the possibility of non-detectabl and/or non-correctable errors resulting from transients.
Another redundant memory system is disclosed in the aforementioned European Patent Application No. 80400603.9. In such patent application, accounting data is written into each of the two non-volatile memories, designated (battery augmented memories) BAMs, twice during each postage meter transaction, once in temporary form and once in permanent form to minimize the loss of accounting data during microcomputer failure.
The aforementioned redundant memory systems may help to eliminate certain errors in the accounting data due to microcomputer failure or the presence of transients. However, since writing into these memories occurs during each transaction or trip cycle of the meter, critical accounting data is written into the non-volatile memories during the noisiest cycle of meter operation when the presence of transients or spurious signals is probably greatest.
A postage meter is described in U.S. patent application Ser. No. 643,219 filed on Aug. 22, 1984 entitled NON-VOLATILE MEMORY SYSEM WITH REAL TIME AND POWER DOWN DATA STORAGE CAPABILITY FOR AN ELECTRONIC POSTAGE METER, now abandoned, issued to the Assignee of the above-mentioned application that describes a method and associated apparatus which increases the reliability of the stored accounting data which reflects the transactions of an electronic postage meter.
In the above-mentioned application, a method and associated apparatus is disclosed which provides a first non-volatile memory which is capable of storing accounting data which represents the postage meter transactions, updating this first non-volatile memory in real time for each postage transaction to provide a current record of the accounting data for each transaction on-the-fly, which provides a second non-volatile memory capable of storing accounting data representing the meter transactions during a power down cycle of the meter, providing a volatile memory capable of storing accounting data which represents the postage meter transactions, updating the volatile memory in real time for each postage transaction and means for transferring the accounting data from the volatile memory to the second non-volatile memory during the power down cycle of the postage meter.
Accordingly, this application provides a system which minimizes errors in the stored accounting data. It also provides a non-volatile memory system for an electronic postage meter in which the accounting data is written into different NVMs during two different cycles of postage meter operation.
It is well known that the non-volatile memories of an electronic postage meter have accounting information within their ascending and descending register locations. This accounting information represents postal funds that have been either entered into or removed from the meter during its operation. It is important that if an electronic postage meter enters a fatal state, the accounting information can be read from the NVMs. The term fatal state means in the context of this description that the meter can no longer operate because of some problem within the circuitry or components of the meter. Accordingly, it is very important that a system be developed for use within an electronic postage meter that can be utilized to access and display certain information that is held within the non-volatile memories.
It is known that in the previous postage meters the non-volatile memory has generally been of the PMOS type such that the method of obtaining the information from the memory is to actually physically extract the device from that meter and to extract the information with another device. This has the disadvantage of preventing ready access to specific information therein. Accordingly, what is needed is a system to determine on a continuing basis the information within the non-volatile memory in an electronic postage meter particularly the accounting information that is located in the ascending and descending register locations.